Electrohydraulic control device

ABSTRACT

An electro-hydraulic control device ( 10, 60 ) for a hydraulic servo motor for controlling a volume flow is proposed, which is embodied as a 4/2 valve module. A blocking valve in accordance with seat valve technology between a motor connection (B) and a return flow (R) form a lowering element ( 11 ), while the associated unblocking member ( 44 ) is designed as a longitudinal slide ( 45 ), which controls the connection between an inflow connection (P) and a motor connection (A) and is actuated by a proportional magnet ( 16 ). After unblocking the blocking valve, its seat valve body ( 23 ) is mechanically taken along by the longitudinal slide ( 45 ), and the two volume flows are proportionally controlled via the lowering element ( 11 ) and the lifting element ( 12 ), so that a large switching capacity is achieved along with a construction with few leaks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is based on an electro-hydraulic control device and, moreparticularly, to an electro-hydraulic control device for a hydraulicservo motor for controlling a volume flow, having a blocking valvearranged in a housing, whose movable seat valve body is inserted into aconnection between a motor chamber and a return flow chamber forsecuring the motor chamber, and having a proportional magnet with anarmature-actuated tappet for actuating the blocking valve.

2. Prior Art

This type of electro-hydraulic control device is already known from U.S.Pat. No. 3,667,722, by means of which a delicate proportional volumecontrol is possible. The check valve protecting the hydraulic servomotor with its load is here designed as a pilot seat valve, so that theleakage is as small as possible. This control device can be used as alowering brake valve, wherein the actuating forces are as low aspossible and therefore the proportional magnet can be made small. It isdisadvantageous in connection with this control device that only a 2/3valve function can be represented, wherein no additional valve functionscan be performed by the lowering element designed in accordance withseat valve techniques. In order to keep the actuating forces low here, aone-armed lever, with which a force transfer is performed, is placedbetween the proportional magnet and the actual seat valve. The force foractuating the check valve is transmitted by an unblocking member, whichis made in a pin shape and with a narrow diameter, so that it cannottake on additional functions. The volume flow appearing during thelowering of a load is here only controlled by a valve cone at a seatvalve body, so that the flow forces appearing particularly at high loadscan considerably interfere with the proportional work functioning of thecheck valve. Therefore the seat valve body, which here is controlledpurely hydraulically, easily tends to oscillate, particularly whenpulling loads or changing load directions occur. The ball in the seatvalve body, which operates as a pilot member, does not have pressurecompensation. In addition, the control device is relatively elaboratelyconstructed, to which the transmitting lever and the valve case for thecheck valve in particular contribute.

Furthermore, an electro-hydraulic control device had already beenproposed in an older patent application, P 195 22 746.8, which operateswith 4/2 valve modules. In this case two such 4/2 valve modules withadditional non-return valves are arranged in a circuit in such a waythat a control valve for a double-acting servo motor results. A seatvalve element and a slide element are combined with each other in each4/2 valve module in such a way, that they have a common, one-piececontrol member. In this not prepublished control device, this one-piececonstruction of the control member in the 4/2 valve module leads to arelatively elaborate construction; in addition, difficulties arise inthis 4/2 valve module because of close longitudinal tolerances whenadjusting the control edges to each other. Form and play tolerances areharder to control with relatively long slides in particular.Furthermore, stepped slides in stepped bores with little play make highdemands in respect to deviations from running true; in addition, thestepped slides cannot be ground centerless.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedelectro-hydraulic control device of the above-described type, especiallyfor a hydraulic servo motor for controlling a volume flow, which doesnot have the above-described disadvantages.

According to the invention the electro-hydraulic control device for ahydraulic servo motor for controlling a volume flow, has a blockingvalve arranged in a housing, whose movable seat valve body is insertedinto a connection between a first motor chamber and a return flowchamber for securing the motor chamber, and has a proportional magnetwith an armature-actuated tappet for actuating the blocking valve, andhas a longitudinally movable unblocking member, which is separated fromthe blocking valve and slidingly guided in the housing, which isinserted into the operation connection between the tappet of theproportional magnet and the blocking valve, and is characterized inthat, the unblocking member and the tappet of the proportional magnetare arranged coaxially with respect to each other and the unblockingmember is embodied as a longitudinal slide which, with one control edge,controls the connection between an inflow chamber and a second motorchamber, wherein the latter is arranged in the slide bore receiving thelongitudinal slide next to the return flow chamber and that thelongitudinal slide essentially has the same exterior diameter as theseat valve body, and that upon actuation by the proportional magnet bothconnections are opened or closed in the same direction.

In contrast hereto, the electro-hydraulic control device of theinvention has the advantage, that with a simple construction itrepresents a 4/2 valve function, wherein a lowering element designed inaccordance with seat valve technology keeps the leakage as small aspossible. The control device can be used in many ways because of its 4/2function, and in addition is constructed in a cost-efficient and compactway. The control device can be employed as a lowering brake valve, bymeans of which a sensitive proportional volume control is possible.Because of the two-piece construction, a control edge adjustment can berealized in a simple manner by the length adaptation of the transferedges.

Advantageous further developments and improvements of theelectro-hydraulic control device possible by means of the measures notedin the dependent claims and the following disclosure.

In a preferred embodiment of the invention the seat valve body and thelongitudinal slide are guided in a continuous slide bore, particularlywith a generally uniform diameter, in which, lying next to each otherand arranged spaced from each other in a direction toward theproportional magnet, four chambers are provided for the first motorconnection, the return flow connection, the second motor connection andthe inflow connection. A valve seat, in particular with a smallerdiameter in comparison with the slide bore, which is associated with theseat valve body, is arranged in this slide bore between the first motorchamber and the return flow chamber. It is possible to achieve aparticularly advantageous compact structure which, with its four workingchambers, is assembled in a particularly space-saving manner.

Other advantageous embodiments are possible in which the blocking valveis a pilot valve, whose seat valve body receives a pilot member, whichcan be unblocked by the longitudinal slide via a transfer bolt.Preferably the pilot member is a pressure-compensated pilot cone. Thismakes it possible to achieve small actuation forces by hydraulicunblocking, so that proportional magnets of small size can be employed.

In another preferred embodiment an axially oriented extension, whichprotrudes into the return flow chamber, has a transfer bolt on its end,and a transfer shoulder associated with the seat valve body is arrangedon the extension. The extension is provided between the longitudinalslide and the seat valve body on one of the two components, preferablyon the longitudinal slide on its side facing away from the proportionalmagnet. In this embodiment the seat valve body and the control slide cancooperate like a mutual, one-piece control member, wherein the controlslide takes the seat valve body along mechanically, as is the case inconnection with a conventional control device. In this case pullingloads in particular can be better managed.

A particularly simple and cost-effective embodiment, which is mainlysuitable for small regulating directional control valves with relativelylow switching capacity, results when the longitudinal slide can bedirectly actuated by the armature tappet, and is pressure-compensatedwith respect to the pressures in the inflow chamber, the second motorchamber and the return flow chamber.

Other embodiments may be used in a wide diversity of possibleapplications. In one of these embodiments a piston section supportingthe control edge on the longitudinal slide has an auxiliary control edgewhich, in an initial position, relieves the second motor chamber intothe return flow chamber, and in an operating position blocks thisconnection. In another embodiment the seat valve body in the slide boredelimits a pressure chamber, in which a spring is arranged which,together with the pressure acting on the front face of the latter,charges the seal valve body in the direction toward the blockingposition, in which it rests with its seat edge, which has a smallerdiameter in comparison with the diameter of the slide bore, against thevalve seat fixed in place on the housing, and in the process encloses anannular chamber, which is located upstream of the valve seat anddelimited by the seat valve body, and whose pressure charges the seatvalve body in the opening direction via an associated annular surface,and which annular chamber is separated from the first motor chamber bymeans of the control edge, on whose pressure charges the seat valve bodyin the opening direction via an associated annular surface, and whichannular chamber is separated from the first motor chamber by means ofthe control edge, on which precision regulating recesses are arranged,particularly located on the circumference of the seat valve body.

In another preferred embodiment the longitudinal slide can be actuatedby the proportional magnet via a hydraulic sequence control device. Thushydraulic amplification is provided for actuating the control slide sothat the control device is suitable for regulating directional controlvalves for higher switching capacities.

This hydraulic amplification can be achieved by a particular simple,cost-effective and compact construction in an embodiment in which thesequence control device has a pilot slide, which can be actuated by theproportional magnet against a regulating spring and is arranged centeredon the longitudinal slide and slidingly guided. Preferably an unblockingpiston is arranged in the longitudinal slide, which is used forunblocking the blocking valve in the lowering element by means of atransfer bolt, which is slidingly guided in the longitudinal slide. Thepilot slide and the unblocking piston preferably have the same exteriordiameter and are slidingly guided in the longitudinal slide in the samelongitudinal bore. The control oil flow, which is used for the hydraulicsequence control device and is conducted from the inflow chamber to thereturn flow chamber, is advantageously conducted over a throttlearranged in the unblocking piston.

A characteristic valve curve can be set when, with its front face facingthe proportional magnet, the longitudinal slide delimits a controlchamber in the slide bore, which chamber receives an adjusting screw,against which the regulating spring is supported, fixed in place on thehousing, which charges the pilot slide against the magnetic force.

BRIEF DESCRIPTION OF THE DRAWING

Two exemplary embodiments of the invention are represented in thedrawings and will be explained in more detail in the followingdescription.

FIG. 1 shows a longitudinal section through a first control device in asimplified representation,

FIG. 2 shows a longitudinal section through a second control device in asimplified representation,

FIG. 3 shows a top view of a portion of the second control device inaccordance with FIG. 2, and

FIG. 4 shows a circuit arrangement with the first, or respectivelysecond control device in accordance with FIG. 1, or respectively 2.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a longitudinal section through a first electro-hydrauliccontrol device 10 in a simplified representation, such as can be usedfor a hydraulic servo motor for the control of volume flows. The controldevice 10 is embodied as a 4/2 valve module, wherein a lowering element11 produced in accordance with seat valve technology and a liftingelement 12 produced in accordance with slide technology are combinedwith each other.

In a housing 13, the control device 10 has a continuous slide bore 14,which is closed at its front faces by a cover 15 and a proportionalmagnet 16. Chambers are formed in the slide bore 14 by means ofring-shaped widenings placed next to each other and embodied in thedirection starting at the cover 15 and viewed in the direction towardthe proportional magnet 16 as a first motor chamber 17, a return flowchamber 18, a second motor chamber 19 and in inflow chamber 21. A firstmotor connection B, a return connection R, a second motor connection Aand an inflow connection P are associated to these chambers 17 to 21 ina corresponding manner. A valve seat 22, whose effective diameter ismade less than the diameter of the slide bore 14, is embodied in theslide bore 14 in the area between the first motor chamber 17 and thereturn flow chamber 18 close to the latter, which valve seat 22represents a part of the lowering element 11.

A pilot seat valve is arranged in the lowering element 11 as a blockingvalve, whose seat valve body 23 is slidingly guided in the slide bore 14and receives a pilot cone 24 in its interior. With its front face 26,which is stressed by a spring 25, the seat valve body 23 delimits apressure chamber 27, whose pressure, together with the force of thespring 25, presses the seat valve body 23 against the valve seat 22. Inthe blocking position, the valve seat body 23 contacts the valve seat 22with a seat edge 28, wherein the diameter of the seat edge 28 is lessthan the diameter of the slide bore 14. The seat valve body 23 is guidedin the slide bore 14 by means of a shaft 29 and on this shaft 29 it hasa first control edge 31, which is followed by precision control recesses32 on the exterior circumference of the shaft 29. An annular chamber 33,to which an annular surface 34 on the seat valve body 23 is assigned, isenclosed in the slide bore 14 by the stepped embodiment of the seatvalve body 23 between the notch-like precision control recesses 32 andthe seat edge 28 of reduced. diameter. The cross section of the slidebore 14, reduced by this annular surface 34, results in a pressure face35, whose size is determined by the effective seat edge 28. The shaft 29is seated with sufficient play in the slide bore 14, so that the loadpressure prevailing in the first motor chamber 17 can also be built upin the pressure chamber 27 and in the annular chamber 33 via the gapsacting as throttle points.

The pilot cone 24 arranged in the seat valve body 23 is designed in apressure-compensated manner, to which end the diameters of its cone edge36 and its shaft section 37 are embodied to be of the same size. Thepilot cone 24 controls the connection from an annular chamber 38 to thereturn flow chamber 18 with its cone edge 36, wherein the annularchamber 38 has a connection with the pressure chamber 27 via a bore 39.By means of the long structure of the shaft element 37, which only has alittle play, the pilot cone 24 seals the annular chamber 38 very wellagainst a spring chamber 41, in which a pilot spring 42 is arranged,which presses the pilot cone 24 on its seat. The spring chamber 41 isconnected with the return flow chamber 18 via conduits 43 arranged inthe pilot cone 24, so that the pilot cone 24 is relieved of pressure onall sides.

An unblocking member 44 has been placed between the pilot blocking valvein the lowering element 11 and the proportional magnet 16, which is heredesigned as a longitudinal slide 45 slidingly arranged in the slide bore14. The longitudinal slide 45 controls the connection between the inflowchamber 21 and the second motor chamber 19 with a second control edge46, wherein notch-like precision control recesses 47 are also arrangedon the second control edge 46. On its end located opposite the precisioncontrol recesses 47, the piston section 48 supporting the second controledge 46 has an auxiliary control edge 49, which controls the connectionfrom the second motor chamber 19 to the return flow chamber 18. Theinflow chamber 21 is blocked by the positive covering of the secondcontrol chamber 46 in the initial position of the longitudinal slide 45represented, while the auxiliary control edge 49 relieves the secondmotor chamber 19 into the return flow chamber 18. The longitudinal slide45 is furthermore pressure-compensated by its annular groove 51 inrespect to the pressure in the inflow chamber 21. The two front faces ofthe longitudinal slide 45 are connected with each other via compensatingbores 52. On its front face facing the proportional magnet 16, thelongitudinal slide 45 rests directly against a tappet 53, actuated bythe armature, of the magnet 16. An extension 54 is formed on theoppositely located front face of the longitudinal slide, which protrudesinto the return flow chamber 18 and which forms a transfer bolt 55 withits trailing end, which rests against the pilot cone 24. The extension54 additionally forms a transfer shoulder 56, which is associated withthe seat valve body 23 and whose contact surface is located at adistance from the end face of the transfer bolt 55.

The functioning of the first control device 10 will be explained asfollows:

With the proportional magnet 16 not excited, the lowering element 11 andthe lifting element 12 take up the initial position represented, whichcorresponds to the neutral position. In this case the inflow connectionP is hydraulically blocked by the longitudinal slide 45, since thesecond control edge 46 blocks the connection to the motor connection A.On the other side the motor connection A is relieved via the auxiliarycontrol edge 49 into the return flow chamber 18, so that no pressure canbuild up in it, even in case of a possibly occurring leak flow. As arule, the servo motor is connected with its load side to the motorconnection B, wherein the pressure in the first motor chamber 17 canalso be built up in the pressure chamber 27 and in the annular chamber38 via the gap formed by the shaft 29. On a remaining differencesurface, which corresponds to the pressure surface 35, the seat valvebody 23 is pressed on the valve seat 22 by the pressure in the pressurechamber 27 and by the force of the spring 25, and in the processprovides a sealing of the motor connection B with few leaks. The loadpressure in the motor connection B can also be built up in the annularchamber 38 from the pressure chamber 27 via the bore 39 where, however,it is dependably sealed in respect to the return flow chamber 18 bymeans of the cone edge 36 and the long shaft of the pilot cone 24. Inthe initial position represented, the pilot spring 42 maintains thepilot cone 24 on its seat, and via the transfer bolt 55 maintains thelongitudinal slide 45 in the position represented, in which it restsagainst the tappet 53 of the proportional magnet 16.

If the proportional magnet 16 is now excited, and in the process thelongitudinal slide 45 is deflected toward the left into the workposition, it first opens the pilot cone 24 by means of the transfer bolt55, by means of which the pressure chamber 27 is relieved into thereturn flow chamber 18. Less pressure medium can flow into the pressurechamber 27 via the gap of the shaft 29 acting as a throttle point, thanflows off via the pilot cone 24, so that the pressure in the pressurechamber 27 is relieved. A pressure possibly still remaining in theannular chamber 33 acts on the annular surface 34 and pushes the seatvalve body 23 toward the left against the force of the spring 25, sothat this annular chamber 33 is relieved into the return flow chamber 18via the seat edge 28. In this way the seat valve body 23 ishydraulically unblocked in this way, and during the left movement of thelongitudinal slide 45 is now taken along by the transfer shoulder 56,which has been placed against the front face of the seat valve body 23.Now the precision control recesses 32 on the seat valve body 23 firstopen and connect the motor connection B with the return flow chamber 18,and thereafter—with negative covering—the precision control recesses 47on the longitudinal slide 45 open the connection from the motorconnection A to the inflow chamber 21. Thus the volume flows, from B toR on the one side, and on the other from P to A, are proportionallycontrolled by means of these precision control recesses. Therefore theswitching capacity of the control device 10 is essentially a function ofthose pressure drops which are effective on the control edges 31, orrespectively 46. It is relatively simple for the lifting element 12 tokeep the pressure drop via the second control edge 46 relatively smalland constant. This can be achieved, for example, by means of a pressurescale, through which a load pressure-compensated volume flow can becontrolled.

The switching load is relatively low at the lowering element 11 when theload pressure is applied at the motor connection B. Because of occurringflow forces, the volume flow flowing through the lowering element 11tries to move the seat valve body 23 toward the right, i.e. to pull itshut. This closing force is all the greater, the greater the volume flowand the pressure drop are. By means of an appropriate layout of theseating angle 58 at the valve seat 22 and of the effective seat diameterit can now be achieved that the pressure is built up in the annularchamber 33. This built-up pressure acts in the annular chamber 33 on anannular surface 34 of the seat valve body 23, and therefore counter tothe flow force. By means of this it is possible to achieve aconsiderable flow force reduction, which leads to an essential increasein the switching capacity even at high load pressures. With the presentcontrol device 10 the seat valve body 23 is mechanically taken alongafter unblocking of the blocking valve, such as is the case per se witha slide device, so that stable functioning can be achieved. Inparticular, in contrast to hydraulically actuated locking blocks,wherein instabilities occur in case of pulling loads, it is possible bymeans of the mechanical coupling of the seat valve body 23 and thelongitudinal slide 45 to achieve stable work conditions even withunfavorable operating conditions. Because of the immediate, directactuation of the longitudinal slide 45 by the proportional magnet 16, avery simple, cost-effective and compact construction results, which canbe advantageously used in particular with smaller switching capacities.Because of the flow force reduction, it is possible in spite of thedirect actuation to achieve a relatively high switching capacity, evenwith relatively small sized proportional magnets. In the workingpositions the proportional magnet 16 pushes the longitudinal slide 45with the seat valve body 23 resting against it to the left against theforce of the spring 25, wherein the size of the stroke is proportionalto the size of the magnetic force. The precision control recesses 32 and47 are actuated corresponding to the amount of deflection, so that thetwo volume flows from B to R, or respectively P to A, are controlledproportionally to the size of the electrical input signal at theproportional magnet 16.

FIG. 2 shows a longitudinal section through a second control device 60,which differs from that in FIG. 1 in the following way, wherein the samereference numerals were used for the same components.

The lowering element 11, the proportional magnet 16 and the slide bore14 with its chambers remain unchanged in the second control device 60,but the lifting element 12 has a different longitudinal slide 61, whichcan be actuated by the proportional magnet 16 via a hydraulic sequencecontrol device 62. In this way the second control device 60 can achievehigher switching capacities in comparison with the first control device10. Here, the longitudinal slide 61 is embodied to be hollow, andreceives a pilot slide 64 in a blind bore-like longitudinal bore 63,which is arranged centered and open toward the proportional magnet 16.The pilot slide 64 is sealingly and slidingly guided by means of apiston section 65 in the longitudinal bore 63 and, together with theradial bore 66 in the longitudinal slide 61, constitutes an adjustablethrottle point 67, which is placed into a control line 68 of thesequence control device 62. This control line 68 leads from the inflowchamber 21 via the radial bores 66, the adjustable throttle point 67,the hollowly embodied pilot slide 64, a portion of the longitudinal bore63, a throttle 62 in an unblocking piston 71 and via oblique bores 72 inthe longitudinal slide 61 into the return flow chamber 18. The pilotslide 64 projects with a cylindrical section 73 into a control chamber74 formed in the slide bore 14 between the longitudinal slide 61 and theproportional magnet 16. An adjusting screw 75, which can be axiallyadjusted by means of a worm, not represented in detail, is arranged inthis control chamber 74, on which a regulating spring 76, which is fixedin place on the housing, is supported, whose other end is supported onthe cylindrical section 73 and maintains the pilot slide 64 in contactagainst the tappet 53 of the proportional magnet 16.

The unblocking piston 71 is slidingly guided at the inner end of thelongitudinal bore 63 of the pilot slide 64 and is in operativeconnection with a transfer pin 77. This transfer pin 77 is slidinglyseated in the extension 54 and rests against the pilot cone 24 of theblocking valve in the initial position of the control device 60. It isparticularly useful here that the pilot slide 64 with its piston section65 and the unblocking piston 71 have the same exterior diameter, so thatthey can be slidingly arranged in a single longitudinal bore 63. In thisway the longitudinal slide 61 makes a one-piece construction possiblebecause of its longitudinal bore 63 embodied in the manner of a blindbore, which is particularly advantageous to produce in connection withproduction technology.

FIG. 3 shows a partial longitudinal section along III—III in FIG. 2,wherein the seat valve body 23, the longitudinal slide 61 and theadjusting screw 75 are shown in a top view.

In principle, the functioning of the second control device 60corresponds to that of the first control device 10 in accordance withFIG. 1, however, greater switching capacities can be achieved because ofthe hydraulic sequence control device 62.

In the represented initial position of the second control device 60,which corresponds to a neutral position, the first motor chamber 17 aswell as the inflow chamber 21 are hydraulically blocked. In the initialposition, the pilot slide 64 is maintained resting against the tappet 53by the regulating spring 76, and thus in a position fixed on thehousing. The axial position of the longitudinal slide 61, which justcloses the adjustable throttle point 67, is also fixed in place in thisway.

When actuating the second control device 60, the proportional magnet 16merely needs to act against the force of the regulating spring 76, sincethe pilot slide 64 is pressure-compensated on all sides. When the pilotslide opens the adjustable throttle point 67, a control oil flow isformed via the control line 68, wherein the pressure built up at thethrottle 69 actuates the unblocking piston 71 and thereby opens thepilot cone 24, so that the blocking valve in the lowering element 11 isunblocked. Otherwise the longitudinal slide 61 follows the stroke of thepilot slide 64, wherein an intermediate pressure builds up in thecontrol chamber 74 for actuating the longitudinal slide 61 and amplifiesthe magnetic force. In the process, the longitudinal slide 61 and thepilot slide 64 work together in a manner known per se in the form of ahydraulic sequence control device. The prestress of the regulatingspring 76 can be changed with the aid of the adjusting screw 75, and theposition of the characteristic valve curve can be set with this.

FIG. 4 shows a circuit in a simplified representation, wherein two firstcontrol devices 10 of FIG. 1 have been arranged to form a directionalcontrol valve 80 for a double-acting servo motor. In this case the two Pconnections of both control devices 10 are connected parallel to acontrol pump 82, while their two connections R are relieved into a tank83. An inflow line 84, or respectively 85, leads from each connection Aof each control device 10 to one of the consumer connections 86, orrespectively 87, on the servo motor 81. Here each inflow line 84, 85 isconducted over a check valve 88, or respectively 89, which protects theload. The two connections B at each control device 10 are respectivelyconnected by means of an outflow line 91, or respectively 92, with therespectively other consumer connection 87, or respectively 86. A loadpressure signal is picked up at the inflow lines 84, 85 and reported tothe control pump 82. A 3-position valve has been realized by means ofthe control valve 80, which securely seals the servo motor 91 when thecontrol devices 10 are not actuated. To keep the leakage low, theconsumer connection 86 is securely blocked on the one side by the checkvalve 88, and on the other side by the blocking valve in the loweringelement 11 of the right control device 10. Similar is true for the otherconsumer connection 87. By actuating the left control device 10, theservo motor 81 can be operated in one direction with the piston rodextending, while by actuating the right control device the servo motor81 can be controlled in the other direction with the piston rodretracting, wherein a proportional operation is achieved. By means ofprocessing the load pressure signal in the control pump 82 it ispossible to keep the pressure drop constant in the lifting element 12via the second control edge 46, so that a load-compensated volume flowcontrol becomes possible.

Changes in the exemplary embodiments represented are of course possiblewithout departing from the scope of the invention. Although the pilotblocking valve in the control device is particularly advantageous, it isalso possible to employ a directly controlled blocking valve having ablocking valve body which has been pressure-relieved to a large extent.The continuous slide bore can also be designed in such a way that in thearea of the lowering element it has a slightly larger diameter than inthe lifting element, so that the interior diameter of the valve seat 22approximately corresponds to the diameter of the slide bore. Also, inthe wiring in accordance with FIG. 4 it is possible to use the secondcontrol devices 60 in place of the first control devices 10. In thiscase the regulating valve 80 can also be embodied in such a way that ithas four operating positions. A constant pump with a pressure scale isalso conceivable in place of the control pump 82.

What is claimed is:
 1. An electro-hydraulic control device for ahydraulic servo motor for controlling a volume flow, having a blockingvalve arranged in a housing, whose movable seat valve body is insertedinto a connection between a first motor chamber and a return flowchamber and in the process secures the motor chamber, and having aproportional magnet with an armature-actuated tappet for actuating theblocking valve, and having a longitudinally movable unblocking member,which is separated from the blocking valve and slidingly guided in thehousing, which is inserted into the operational connection between thetappet of the proportional magnet and the blocking valve, characterizedin that the seat valve body (23), the unblocking member (44) and thetappet (53) of the proportional magnet (16) are arranged coaxially inrespect to each other, and the unblocking member is embodied as alongitudinal slide (45, 61) which, with one control edge (46), controlsthe connection between an inflow chamber (21) and a second motor chamber(19), wherein the latter is arranged in the slide bore (14) receivingthe longitudinal slide (45, 61) next to the return flow chamber (18),and that the longitudinal slide (45, 61) essentially has the sameexterior diameter as the seat valve body (23), and that upon actuationby the proportional magnet (16), both connections are opened or closedin the same direction.
 2. The electro-hydraulic control device inaccordance with claim 1, characterized in that the blocking valve is apilot valve, the seat valve body (23) receives a pilot member (24) andthe pilot member (24) is opened by the longitudinal slide (45,61) via atransfer bolt (55,77).
 3. The electro-hydraulic control device inaccordance with claim 2, characterized in that the pilot member is apressure-compensated pilot cone (24).
 4. The electro-hydraulic controldevice in accordance with claim 1, characterized in that thelongitudinal slide (45) has notch-like precision regulating recesses(47) on said control edge (46).
 5. The electro-hydraulic-control devicein accordance with claim 1, characterized in that the longitudinal slide(61) can be actuated by the proportional magnet (16) via a hydraulicsequence control device (62) (FIG. 2).
 6. The electro-hydraulic controldevice in accordance with claim 5, characterized in that the sequencecontrol device (62) has a pilot slide (64), which can be actuated by theproportional magnet (16) against a regulating spring (76) and isarranged centered on the longitudinal slide (61) and slidingly guided.7. The electro-hydraulic control device in accordance with claim 6,characterized in that the pilot slide (64) is embodied to bepressure-compensated.
 8. The electro-hydraulic control device inaccordance with claim 5, characterized in that an unblocking piston (71)is arranged in the longitudinal slide (61), which is used for unblockingthe blocking valve in the lowering element (11) by means of a transferbolt (77), which is slidingly guided in the longitudinal slide. 9.Theelectro-hydraulic control device in accordance with claim 8,characterized in that the control oil flow, which is used for thehydraulic sequence control device (62) and is conducted from the inflowchamber (21) to the return flow chamber (18), is conducted over athrottle (69) arranged in the unblocking piston (71).
 10. Theelectro-hydraulic control device in accordance with claim 5,characterized in that the pilot slide (64) and the unblocking piston(71) have the same exterior diameter and are slidingly guided in thelongitudinal slide (63) in the same longitudinal bore (63).
 11. Theelectro-hydraulic control device in accordance with claim 5,characterized in that, with its front face facing the proportionalmagnet (16), the longitudinal slide (61) delimits a control chamber (74)in the slide bore (14), which chamber receives an adjusting screw (75),against which the regulating spring (76) is supported, fixed in place onthe housing, which charges the pilot slide (64) against the magneticforce.
 12. The electro-hydraulic control device in accordance with claim5, characterized in that the control line (68) associated with thehydraulic sequence control device (62) is conducted through the hollowpilot slide (64), the longitudinal bore (63) and the unblocking piston(71), wherein the pressure is supplied to the control chamber (74)upstream of the throttle (69) and downstream of an adjustable throttlingpoint (67) and drives the longitudinal slide.
 13. The electro-hydrauliccontrol device in accordance with claim 1, characterized in that theseat valve body (23) and the longitudinal slide (45,61) are guided in acontinuous slide bore (14); the first motor chamber (17), the returnflow chamber (18), the second motor chamber (19) and the inflow chamber(21) are formed by four widenings provided in the slide bore (14) andaranged spaced from each other in a direction toward the proportionalmagnet (16); the four chambers (17,18,19,21) are associated with a firstmotor connection (B), a return flow connection (R), a second motorconnection (A) and an inflow connection (P) respectively; and a valveseat (22) having a diameter smaller than that of the slide bore (14),said valve seat (22) being associated with the seat valve body (23), isarranged in the slide bore (14) between the first motor chamber (17) andthe return flow chamber (18).
 14. The electro-hydraulic control devicein accordance with claim 13, characterized in that the seat valve body(23) in the slide bore (14) bounds a pressure chamber (27), in which aspring (25) is arranged, and the seat valve body (23) is urged in adirection toward a blocking position by the spring (25) and a pressurein the pressure chamber (27) acting on a front face of the seat valvebody (23) with a seat edge (28) thereof resting against the valve seat(22) fixed on the housing so as to form an annular chamber (33) upstreamof the valve seat and bounded by the seat valve body, and a pressure inthe annular chamber (33) urges the seat valve body in an openingdirection via an associated annular surface (34), said annular chamber(33) being separated from the first motor chamber (17) by means of thecontrol edge (31), in which regulating recesses (32) are provided arounda circumference of the seat valve body.
 15. The electro-hydrauliccontrol device in accordance with claim 1, characterized in that thelongitudinal slide (45,61) has an axially oriented extension (54) at anend of the longitudinal slide (45,61) facing away from the proportionalmagnet (16) and the axially oriented extension (54) protrudes into thereturn flow chamber (18), the extension (54) has a transfer shoulder(56) associated with the seat valve body (23) and the extension (54) hasa transfer bolt (55,77) at an end of the extension (54).
 16. Theelectro-hydraulic control device in accordance with claim 1,characterized in that the longitudinal slide (45) is directly operableby means of the armature tappet (53) and further comprising means forpressure compensating pressures present in the inflow chamber (21), thesecond motor chamber (19) and the return flow chamber (18).
 17. Theelectro-hydraulic control device in accordance with claim 1,characterized in that the longitudinal slide (45) has a piston section(48) supporting said control edge (46) and an auxiliary control edge(49), which, in an initial position, relieves the second motor chamber(19) to the return flow chamber (18), and in an operating positionblocks this connection.